The concept of a core charge doesn't apply here because with a core charge, the seller isn't out anything. They could simply give the buyer credit (money) when the buyer brings their old part to them because they can turn around and send the part to a manufacturer in exchange for money.
Sellers do charge a core charge, however, because they want that money.
In your case, you are out something. You pay for a fancy container and want to get that back. If you don't get it back, you want to at least recoup the money you paid for it.
So...
You have to charge up front for the container and refund when you get it back. If you don't get it back, you have the money they paid upfront. You're in a one-down situation from the core charge scenario, but it can work if you charge for the expense up front and refund when/if you get it back.
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